Thanks for pointing this out.
You could very easily be right with respect to gcc being allowed to run in parallel. That means we've got another problem. I can't speak for Inline::C's test suite, but I can say that no Inline::CPP test is intentionally reliant on any other test. And to answer your question, Inline::CPP generates within an _Inline directory a new subdirectory for each build's files. Nevertheless, there must be some resource that is getting clobbered, and I should be investigating that instead of looking for a means of preventing parallel testing. More research needed in that area, it seems.
Let's put the Inline::CPP example aside for a moment then, and let the original question stand without any strong example of a module that fits that infinitesimally small category. :)
